At the summary trial of offenses against the laws for the protection of persons or property engaged in commerce or navigation, it shall not be necessary that the accused shall have been previously indicted, but a statement of complaint, verified by oath in writing, shall be presented to the court, setting out the offense in such manner as clearly to apprise the accused of the character of the offense complained of, and to enable him to answer the complaint. The complaint or statement shall be read to the accused, who may plead to or answer the same, or make a counterstatement. The trial shall thereupon be proceeded with in a summary manner, and the case shall be decided by the court, unless, at the time for pleading or answering, the accused shall demand a jury, in which case the trial shall be upon the complaint and plea of not guilty.